1. Field of the Invention
The invention relates generally to the field of photography, and more particularly to a film cassette containing roll film.
2. Description of the Prior Art
In the standard 35 mm film manufacturers' cassette, such as manufactured by Eastman Kodak Co. and Fuji Photo Film Co., Ltd., the filmstrip is wound on a flanged spool which is rotatably supported within a cylindrical shell. A leading end section of the filmstrip approximately 21/3 inches long, commonly referred to as a "film leader", protrudes from a light-trapped slit or mouth of the cassette shell. One end of the spool has a short axial extension which projects from the shell, enabling the spool to be turned by hand. If the spool is initially rotated in an unwinding direction, the film roll inside the shell will tend to expand radially since the inner end of the filmstrip is attached to the spool, and the fogged leader section protruding from the slit will remain stationary. The film roll can expand radially until a non-slipping relation is established between its outermost convolution and the inner curved wall of the shell. Once this non-slipping relation exists, there is a binding effect between the film roll and the shell which prevents further rotation of the spool in the unwinding direction. Thus rotation of the spool in the unwinding direction cannot serve to advance the filmstrip out of the shell, and it is necessary in the typical 35 mm camera to engage the protruding leader section to draw the filmstrip out of the shell.
Representative patent art is as follows:
(a) U.S. Pat. No. 988,341, patented Apr. 4, 1911, discloses a film spool having a pair of coaxially spaced flanges between which a film and paper roll is wound on the spool to form alternating convolutions of photographic film and paper. The film and paper roll appears to be very tightly wound on the spool to prevent ambient light from reaching the successive film convolutions. Several dimples positioned on the respective undersides of the two flanges firmly secure the outermost film convolution and the outermost paper convolution in place to prevent their movement with respect to the dimples. This is done to maintain the tight winding of the roll. When the spool is loaded in a camera, it must be done in subdued light because the outermost film convolution and the outermost paper convolution have to be manually disengaged from the several dimples in order to secure the film and paper leading ends to a take-up means. However, disengagement of the outermost film and paper convolutions from the dimples might allow the roll to unwind or clock-spring about the spool. Thus the facility of the roll to light-shield the successive film convolutions would be lost.
(b) U.S. Pat. No. 3,797,777, patented Mar. 19, 1974, discloses a tape storage magazine containing a rotatable reel having a pair of coaxially spaced flanges between which a magnetic tape roll is tightly wound on the spool. The outermost tape convolution between the two flanges is connected to, though is spaced from, the innermost convolution of a wider stiffer leader tightly coiled at the circumferential edges of the flanges. A number of flexible fingers integrally formed with at least one of the flanges radially extend beyond the circumferential edges(s) of the flange(s) to transversely pinch the contiguous leader convolutions to prevent them from contacting the magazine wall. The forward end of the stiffer wider leader is positioned within the storage magazine and it slightly extends beyond the range of the flexible fingers. When the reel is rotated in an unwinding direction, the flexible fingers propel the outermost leader convolution past a stationary disengaging member to strip successive sections of the wider leader from engagement with the respective fingers. The flexible fingers where engaged with the contiguous leader convolutions serve to thrust the freed leader sections along a predetermined threading path from the storage magazine. However, since the tape leader must be grabbed by the flexible fingers with a sufficient force to thrust the freed leader sections along the threading path, it is possible that the fingers may damage the tape leader, in which instance a leader jam could result.